Atomistic Simulations of Calcium Uranyl(VI) Carbonate Adsorption on Calcite and Stepped-Calcite Surfaces

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• 作者：Slimane Doudou ; David J. Vaughan ; Francis R. Livens ; Neil A. Burton
• 刊名：Environmental Science & Technology (ES&T)
• 出版年：2012
• 出版时间：July 17, 2012
• 年：2012
• 卷：46
• 期：14
• 页码：7587-7594
• 全文大小：350K
• 年卷期：v.46,no.14(July 17, 2012)
• ISSN：1520-5851

文摘

Adsorption of actinyl ions onto mineral surfaces is one of the main mechanisms that control the migration of these ions in environmental systems. Here, we present computational classical molecular dynamics (MD) simulations to investigate the behavior of U(VI) in contact with different calcite surfaces. The calcium-uranyl-carbonate [Ca₂UO₂(CO₃)₃] species is shown to display both inner- and outer-sphere adsorption to the flat {101虆4} and the stepped {314虆8} and {31虆2̅16} planes of calcite. Free energy calculations, using the umbrella sampling method, are employed to simulate adsorption paths of the same uranyl species on the different calcite surfaces under aqueous condition. Outer-sphere adsorption is found to dominate over inner-sphere adsorption because of the high free energy barrier of removing a uranyl鈥揷arbonate interaction and replacing it with a new uranyl鈥搒urface interaction. An important binding mode is proposed involving a single vicinal water monolayer between the surface and the sorbed complex. From the free energy profiles of the different calcite surfaces, the uranyl complex was also found to adsorb preferentially on the acute-stepped {314虆8} face of calcite, in agreement with experiment.